Henry Collins Flagg was born on August 21, 1742, in Newport, Rhode Island, into a family connected with the town’s maritime and professional society. The names and circumstances of his parents are not consistently detailed in brief public biographies, but his later career indicates access to education and respectable family support. Newport was one of colonial America’s busiest ports, shaped by shipping, craft production, privateering, Atlantic trade, religious diversity, slavery, and the slave trade. Flagg trained in medicine during an era before standardized medical schools. A prospective physician normally learned through apprenticeship with an established practitioner, extensive reading, observation, and the preparation of drugs. Some also attended lectures or traveled abroad. The exact sequence of Flagg’s training requires more documentation, but he acquired sufficient skill to establish a medical practice. He also became interested in military affairs and joined local militia activity. Newport’s strategic location and memories of earlier imperial wars made martial preparation familiar to young men of his generation. Medical knowledge and militia service could readily overlap, since armies urgently needed surgeons capable of treating wounds, disease, and the effects of poor camp conditions. Flagg married and built family and community connections before or during the Revolutionary era. When conflict began, he supported the Patriot cause and served as a surgeon and officer. His work demanded both professional judgment and personal courage, particularly in environments where supplies were scarce and infection poorly understood. Before gaining Revolutionary notice, Flagg had been shaped by a cosmopolitan seaport, practical medical education, local professional networks, and militia culture. Surviving records reveal more about his service than his childhood, so undocumented family anecdotes should not be supplied. The firmest interpretation of his early life is occupational: Newport provided the maritime, intellectual, and military environment in which an educated young man could combine medicine with public service.